linux-kernel - [PATCH 09/10 v2] drm/i915/intel_i2c: reuse GMBUS2 value read in polling loop

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Date:	Sat, 10 Mar 2012 02:48:23 +0800
From:	Daniel Kurtz <djkurtz@...omium.org>
To:	Keith Packard <keithp@...thp.com>, David Airlie <airlied@...ux.ie>,
	Daniel Vetter <daniel@...ll.ch>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:	Benson Leung <bleung@...omium.org>,
	Yufeng Shen <miletus@...omium.org>,
	Sameer Nanda <snanda@...omium.org>,
	Daniel Kurtz <djkurtz@...omium.org>
Subject: [PATCH 09/10 v2] drm/i915/intel_i2c: reuse GMBUS2 value read in polling loop

Save the GMBUS2 value read while polling for state changes, and then
reuse this value when determining for which reason the loops were exited.
This is a small optimization which saves a couple of bus accesses for
memory mapped IO registers.

Signed-off-by: Daniel Kurtz <djkurtz@...omium.org>
Reviewed-by: Chris Wilson <chris@...is-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_i2c.c |   19 ++++++++++---------
 1 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 61fe317..2c372d3 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -243,6 +243,7 @@ gmbus_xfer(struct i2c_adapter *adapter,
 	struct drm_i915_private *dev_priv = adapter->algo_data;
 	int i, reg_offset;
 	int ret = 0;
+	u32 gmbus2 = 0;
 
 	if (bus->force_bit)
 		return intel_i2c_quirk_xfer(dev_priv,
@@ -296,12 +297,12 @@ gmbus_xfer(struct i2c_adapter *adapter,
 			do {
 				u32 val, loop = 0;
 
-				if (wait_for(I915_READ(GMBUS2 + reg_offset) &
+				if (wait_for((gmbus2 = I915_READ(GMBUS2 +
+								 reg_offset)) &
 					     (GMBUS_SATOER | GMBUS_HW_RDY),
 					     50))
 					goto timeout;
-				if (I915_READ(GMBUS2 + reg_offset) &
-				    GMBUS_SATOER)
+				if (gmbus2 & GMBUS_SATOER)
 					goto clear_err;
 
 				val = I915_READ(GMBUS3 + reg_offset);
@@ -335,21 +336,21 @@ gmbus_xfer(struct i2c_adapter *adapter,
 				I915_WRITE(GMBUS3 + reg_offset, val);
 				POSTING_READ(GMBUS2 + reg_offset);
 
-				if (wait_for(I915_READ(GMBUS2 + reg_offset) &
+				if (wait_for((gmbus2 = I915_READ(GMBUS2 +
+								 reg_offset)) &
 					     (GMBUS_SATOER | GMBUS_HW_RDY),
 					     50))
 					goto timeout;
-				if (I915_READ(GMBUS2 + reg_offset) &
-					      GMBUS_SATOER)
+				if (gmbus2 & GMBUS_SATOER)
 					goto clear_err;
 			}
 		}
 
-		if (wait_for(I915_READ(GMBUS2 + reg_offset) &
+		if (wait_for((gmbus2 = I915_READ(GMBUS2 + reg_offset)) &
 			     (GMBUS_SATOER | GMBUS_HW_WAIT_PHASE),
 			     50))
 			goto timeout;
-		if (I915_READ(GMBUS2 + reg_offset) & GMBUS_SATOER)
+		if (gmbus2 & GMBUS_SATOER)
 			goto clear_err;
 	}
 
@@ -373,7 +374,7 @@ clear_err:
 	ret = -ENXIO;
 
 done:
-	if (I915_READ(GMBUS2 + reg_offset) & GMBUS_HW_WAIT_PHASE) {
+	if (gmbus2 & GMBUS_HW_WAIT_PHASE) {
 		I915_WRITE(GMBUS1 + reg_offset,
 			   GMBUS_CYCLE_STOP | GMBUS_SW_RDY);
 		POSTING_READ(GMBUS2 + reg_offset);
-- 
1.7.7.3

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